Fatty acid alkyl ester is widely used in the fields of cosmetics and medicines, as well as fatty acid alkyl ester derived from animal fats and vegetable oils is used in foods. Further, attention is paid to fatty acid alkyl ester serving as a fuel to be added to gas oil. In other words, this is a biodiesel fuel derived from animal fats and vegetable oils, which has been developed in order to reduce the amount of carbon dioxide to be exhausted. Fatty acid alkyl ester is directly used as a substitute for gas oil etc., or used as a fuel to be added to gas oil etc. with a certain ratio. The biodiesel fuel has various advantages such that it gives less damage to environment compared with a conventional diesel fuel derived from petroleum.
Further, glycerin is used mainly as a raw material for nitroglycerin, and also used in various fields such as a raw material for alkyd resin, medicines, foods, printing ink, cosmetics etc.
An example of a method for producing such fatty acid alkyl ester and glycerin is a method in which triglyceride that is a main component of fat and oil is subjected to ester exchange with alcohol.

where R represents an alkyl group having 6-22 carbon atoms or an alkenyl group having 6-22 carbon atoms with one or more unsaturated bonding.
In general, as the method with use of a transesterification between fats and oils and alcohols, a method using a homogeneous alkaline catalyst is industrially used.
However, usage of a homogeneous alkaline catalyst makes a step of separating and removing a catalyst complicated. Further, free fatty acid included in fat and oil is saponified by the alkaline catalyst and consequently a soap is produced as a by-product. This requires a step of cleaning the soap with a large amount of water and decreases the yield of fatty acid alkyl ester due to emulsification of the soap. Further, a step of refining glycerin is complicated.
In order to solve the problem, there have been developed methods for producing fatty acid alkyl ester and/or glycerin over a solid catalyst instead of a homogeneous alkaline catalyst (see Patent Documents 1-5 for example). The method using the solid catalyst has a less complicated process, and has a less amount of wastes such as waste water and waste salts produced in the reaction, compared with the method using the homogeneous alkaline catalyst. Further, Patent Document 6 discloses a method for producing fatty acid alkyl ester and/or glycerin over a solid catalyst.
Production of fatty acid alkyl ester and glycerin over the solid catalyst does not require a complicated operation in its production process, and has a less amount of wastes such as waste water and waste salts produced in the reaction, compared with the method using the homogeneous alkaline catalyst.
However, in general, a transesterification is an equilibrium reaction. Therefore, both in a case of the homogeneous alkaline catalyst and a case of the solid catalyst, it is necessary to use an excessive amount of a raw material (alcohol in general) in order to obtain a high yield of a product.
Recently, in view of consideration on environment and reduction of costs for production, it is requested that a material that can be reused by reproduction is reused as far as possible. Therefore, in producing fatty acid alkyl ester and glycerin, it is requested that out of an excessive amount of alcohol used in the transesterification, unreacted alcohol that remains without being used in the reaction is separated and refined from a reaction liquid so as to be reused as a raw material. For example, Patent Document 7 discloses a method in which unreacted alcohol that remains without being used in a reaction is evaporated from a reaction liquid by a pressure flash and then refined as alcohol through evaporation and reused as a raw material for a transesterification.    Patent Document 1: Japanese Unexamined Patent Publication No. Tokukai 2005-200398 (published on Jul. 28, 2005)    Patent Document 2: Japanese Unexamined Patent Publication No. Tokukai 2006-225352 (published on Aug. 31, 2006)    Patent Document 3: Japanese Unexamined Patent Publication No. Tokukai 2005-177722 (published on Jul. 7, 2005)    Patent Document 4: Japanese Unexamined Patent Publication No. Tokukaihei 7-173103 (published on Jul. 11, 1995)    Patent Document 5: French Patent Publication No. 2752242, specification    Patent Document 6: Japanese Unexamined Patent Publication No. Tokukai 2005-206575 (published on Aug. 4, 2005)    Patent Document 7: U.S. Unexamined Patent Publication No. 2004/0034244, specification    Patent Document 8: U.S. Unexamined Patent Publication No. 2005/0113588, specification